Method of controlling airflow through an air diffuser

ABSTRACT

In an air conditioning system the rate of airflow through a diffuser is controlled by varying the permitted travel of the air flow control disc. The disc is displaceable between a fully opened position in which the maximum designed airflow through the diffuser occurs and a fully closed position in which the minimum designed air flow through the diffuser occurs. The method of the present invention comprises sensing duct pressure at the diffuser and adjusting the limits of travel of the air flow control disc. Adjustment is in the direction which restricts the permitted travel of the disc towards the fully closed position and allows travel of the disc beyond the fully open position in the event that a pressure below designed duct pressure is detected. Adjustment is to permit travel of the disc beyond the fully closed position and restrict travel of the disc towards the fully opened position in the event that a pressure above designed duct pressure is detected in the ducting.

FIELD OF THE INVENTION

This invention relates to a method of controlling air flow through an air diffuser of an air conditioning system.

BACKGROUND TO THE INVENTION

Air diffusers are used in air conditioning systems to distribute cooled air to one or more air-conditioned rooms. Automatic air diffusers are configured to use the room temperature as input and to control the rate at which air is supplied to each room. If the room temperature is warmer than the required temperature, the supply of air is increased to bring the room temperature down. If the room is too cold the supply of air is decreased to allow the temperature to rise. In air-conditioning parlance, the decrease in the supply of air to let the air temperature rise is referred to as heating although no heated air is supplied.

Apart from the need to maintain temperatures in air-conditioned rooms, there are typically also ventilation requirements. Sufficient fresh air needs to be supplied to maintain adequate oxygen and/or to remove harmful gases such as carbon dioxide irrespective of whether or not a room needs to be heated or cooled. However, excessive ventilation is also not desirable, because it wastes energy, with no real benefit.

Current automated air-conditioning systems are designed to distribute adequate fresh air to each air-conditioned room and to maintain the temperature in each room within predetermined parameters.

Simply by way of example, maximum airflow can be set at 100 L per minute and minimum air flow can be set at 30 L per minute.

In earlier air-conditioning systems, mechanical stops limited the movement of the disc of the diffuser. When the disc was in the fully open position and the pressure in the duct was at design pressure, the full volume of 100 L per minute flowed through. When against the other stop, the disc was in the fully closed position and, again if the duct was at design pressure, let through the requisite volume of 30 L per minute.

To adjust the stops it was necessary for a technician to be at the diffuser and physically to move the stops. The permitted travel of the disc was consequently changed.

With the advent of computer controls and the use of stepping motors, the ends stops became “software ends stops” rather than mechanical end stops. Detectors sense the position of the disc and the software switches-off the stepping motor when the allowed travel of the disc in a specific direction has been reached. These stops were still, however, fixed in the sense that they restricted travel of the disc between two immovable end limits.

The provision of the stops in these systems is to prevent excessive quantities of air being supplied as would happen if the disc moved past its normal fully open position. If the disc moves beyond its normal fully closed position, the quantity of air required to prevent room air becoming stale and unhygienic would not be supplied.

The ducting of an air conditioning system is designed so that the pressure is constant throughout the ducting. The air moving fan of the system is selected so that it supplies sufficient air to maintain the designed air pressure in the ducting.

Should, however, the pressure in the ducting change, or not be at design pressure at a specific diffuser, the intended rate of air flow through that diffuser at fully opened or fully closed is not achieved.

The present invention provides a method of ensuring that airflow through each diffuser of the system, at both fully opened and fully closed positions, is at the rate called for by the system's design parameters.

BRIEF DESCRIPTION OF THE INVENTION

According to the present invention there is provided a method of operating an air conditioning system which includes controlling the rate of airflow through a diffuser by controlling the permitted travel of the air flow control element which is displaceable between a fully opened position in which the maximum designed airflow through the diffuser occurs and a fully closed position in which the minimum designed air flow through the diffuser occurs, the operating method comprising sensing duct pressure at the diffuser during day-to-day operation of the air conditioning system and adjusting the limits of travel of the air flow control element in the direction which restricts the permitted travel towards the fully closed position and allows travel beyond the fully open position in the event that a pressure below designed duct pressure is detected, and permits travel beyond the fully closed position and restricts travel towards the fully opened position in the event that a pressure above designed duct pressure is detected in the ducting.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:

FIG. 1 diagrammatically illustrates the way in which air flow is controlled when the pressure is above designed duct pressure; and

FIG. 2 diagrammatically illustrates the way in which air flow is controlled when the pressure is below designed duct pressure.

DETAILED DESCRIPTION OF THE INVENTION

The ducting of an air-conditioning system is designed so that, as far as possible, the pressure throughout the ducting is constant. If this is achieved, then the rate of air flow through each diffuser, when the movable air flow control discs are identically positioned, is the same.

When duct pressure is at the pressure for which the system is designed (hereinafter referred to as “designed duct pressure”) the disc has a normal fully open position and a normal fully closed position. These positions will be referred to as the designed fully open position and the designed fully closed position. In the designed fully open position at designed duct pressure the maximum volume of air for which the system is designed flows through the diffuser. As indicated this could be, for example, 100 L per minute.

In the designed fully closed position at designed duct pressure, ventilating air flow of, for example, 30 L per minute is permitted.

The air moving fan provides sufficient air to ensure that there is constant pressure in the ducting. However, in practice there are always variations in ducting pressure. The better the design of the ducting is, the less the variations. Pressure variations of up to 30% can occur if the ducting is not optimally designed.

The effect of this is that, at the designed fully open position, too much air flows through the diffuser if the pressure is high and the temperature in the room being air-conditioned drops. The temperature control loop then moves the disc to restrict air flow to the room and limit the fall in temperature. However, in this situation other diffusers may be deprived of air due to the flow through that diffuser at which there is an above design pressure. Likewise at the designed fully closed position, an overpressure in the duct results in too much air flowing through that diffuser into the room and it does not warm up as it is required.

Conversely, a duct pressure below design pressure has the effect that too little air is supplied at designed fully open to maintain the requisite room temperature which consequently tends to rise. At the design fully closed position, there is inadequate airflow to ventilate the room and again the temperature tends to increase. In both instances the temperature control loop will attempt to drive the disc in the direction which allows more air to flow.

In accordance with the present invention the pressure in the duct immediately adjacent the diffuser is continuously sensed whilst the air-conditioning system is in day-to-day operation for the purpose of controlling the temperature in the room that the diffuser feeds.

The computer controlling the air conditioning system at intervals interrogates the pressure sensor and the then current pressure in the duct is read.

If a pressure above designed duct pressure is detected, the control system adjusts the two “end of travel” stops of the movable disc. The effect of this is that the disc is permitted to move, in the closing direction, to a position beyond that which it occupies when in the fully closed design position, that is, when the duct pressure is equal to designed duct pressure. The effect is to reduce the area of the flow passage to the room to less than the area at designed fully closed and consequently restrict the volume of air that can flow in as a result of the higher pressure.

In the opening direction, in an overpressure condition in the duct, the disc is restricted from moving to the position it occupies when it is in the designed fully open position and duct pressure is at the requisite level. The area through which air can flow is thus less than the area available for flow when the disc is at its designed fully open position at the correct duct pressure.

In the event of a pressure in the ducting less than the designed duct pressure, the “end of travel” stops set in the computer program are again moved. In the closing direction the disc is prevented from moving to the designed fully closed position it occupies when the duct is at the correct pressure. The area through which air can flow is consequently greater than it is when the disc is in its designed fully closed position at correct duct pressure. This makes it possible for the requisite quantity of air to flow through even at the reduced duct pressure.

Conversely, in the opening direction, the stop is moved so that the disc is permitted to travel beyond the designed fully open position. The area available for air flow is consequently increased and the requisite quantity of air can flow even in conditions of low duct pressure.

In the drawings, FIG. 1 diagrammatically illustrates the disc of the diffuser in various positions designated 10.1, 10.2 etc, the cone 12 in which the disc 10 moves and the duct 14 which leads to the upper end of the cone 12. The mechanism which moves the disc 10 has not been illustrated.

The positions of the disc designated 10.1 and 10.2 are the fully closed and fully open conditions of the diffuser. When pressure in the duct 14 is at designed duct pressure, the disc can move between the fully open and fully closed positions 10.1, 10.2. It will be noted that in what is called the fully closed condition 10.1 there is some flow through the diffuser between the periphery of the disc and the inner surface of the cone 12.

If the duct pressure is above designed duct pressure, then flow through the diffuser is greater than required. The end stops are, in these circumstances, shifted so that the disc can move to the position 10.3 where it has travelled beyond the fully closed position. This restricts air flow to below that which is possible when there is an over-pressure condition and the disc is at 10.1. The other stop restricts the disc's movement towards the fully open position and prevents movement beyond 10.4.This again reduces the air flow below that which is possible when the disc is at 10.2 and there is an over-pressure condition.

For the purposes of FIG. 2 it is assumed that there is an under-pressure condition. When the disc is at 10.1 the flow is lower than it should be due to the under-pressure condition. The disc's movement is restricted by the stop so that it can only move to the position 10.5 thereby allowing more air to flow. In the fully open direction the disc is permitted to move to position 10.6 so the open area of the diffuser is greater and there is an increased airflow. 

1. A method of operating an air conditioning system which includes controlling the rate of airflow through a diffuser by controlling the permitted travel of the air flow control element which is displaceable between a fully opened position in which the maximum designed airflow through the diffuser occurs and a fully closed position in which the minimum designed air flow through the diffuser occurs, the operating method comprising sensing duct pressure at the diffuser during day-to-day operation of the air conditioning system and adjusting the limits of travel of the air flow control element in the direction which restricts the permitted travel towards the fully closed position and allows travel beyond the fully open position in the event that a pressure below designed duct pressure is detected, and permits travel beyond the fully closed position and restricts travel towards the fully opened position in the event that a pressure above designed duct pressure is detected in the ducting. 